The present disclosure generally relates to optical computing, and, more specifically, to optical analysis tools having an operational profile that is smaller than that conventionally attainable.
Spectroscopic analyses are well known for their versatility for detecting a wide variety of substances. Most spectroscopic instruments are general purpose and are not configured to detect any one particular substance or class of substance. Accordingly, involved and time-consuming spectral processing and/or sample preparation operations may be needed to analyze for a particular substance within a given sample. Although spectroscopic analyses can often be routinely carried out under regulated laboratory conditions, they can be considerably more difficult to transition into less controlled environments, such as the oilfield and other process settings, where operational conditions may damage and/or limit the accuracy of conventional spectroscopic equipment and techniques.
Optical computing devices represent an alternative to conventional spectroscopic equipment and techniques. As used herein, the term “optical computing device” will refer to an optical device configured to receive an input of electromagnetic radiation from a sample and produce an output of electromagnetic radiation from a processing element that is diagnostic of a characteristic of the sample. Optical computing devices utilize an integrated computational element (ICE), also referred to as an “ICE core,” which is a processing element that is specifically designed to analyze for a given component or characteristic of interest in a sample upon optical interaction of electromagnetic radiation therewith. As used herein, the term “integrated computational element” will refer to an optical processing element containing a plurality of optical thin film layers formed from various materials whose indices of refraction and thicknesses may vary between each layer. The layer compositions, thicknesses, and ordering may be chosen, based upon calculations, to selectively transmit or reflect predetermined fractions of electromagnetic radiation at different wavelengths such that the integrated computational element is configured to substantially mimic the regression vector corresponding to a particular component or characteristic of interest in a sample.
As used herein, the term “characteristic” will refer to a substance's concentration in a sample or a derived physical property for the sample. The transmission or reflection function of the integrated computational element may represent the regression vector for a characteristic of interest, and the transmission or reflection function may be weighted with respect to wavelength. Accordingly, upon optically interacting electromagnetic radiation with a sample and with an integrated computational element, the electromagnetic radiation may change in a known and specific way that may be representative of the characteristic's magnitude in the sample. Following receipt of the electromagnetic radiation by a detector, an output from the detector can be correlated to the characteristic of interest, optionally after additional computational processing takes place. Even though a complex mixture of substances may be present in a given sample, the integrated computational element may be able to distinguish and analyze for a particular substance or characteristic based on the unique regression vector represented by the integrated computational element.
Optical computing devices may be advantageous compared to conventional spectroscopic techniques, since optical computing analyses may be conducted rapidly, often in real-time, with limited to no sample preparation involved. Rather than obtaining an optical spectrum as in conventional spectroscopic techniques, which may require further interpretation and deconvolution to take place, the output of optical computing devices is a real number that is correlatable to a characteristic of interest. Optical computing devices are also much more rugged than conventional spectroscopic equipment and can be deployed in locales where spectroscopic analyses may otherwise be problematic. Accordingly, optical computing devices may often be desirable for analyzing complex mixtures in various process environments, such as those encountered in the oilfield industry.
Optical computing analyses may utilize a single integrated computational element or, more commonly, a plurality of integrated computational elements. A plurality of integrated computational elements may be used to analyze for multiple characteristics of a sample or a single sample characteristic. Using multiple integrated computational elements to analyze for a single sample characteristic may involve optically interacting electromagnetic radiation with the sample and with multiple integrated computational elements in sequence or by computationally combining the outputs of two or more integrated computational elements with one another. Benefits that may be realized when utilizing multiple integrated computational elements in the analysis of a single characteristic of interest include, but are not limited to, increased analytical sensitivity, signal normalization and combinations thereof.
Conventional optical computing device configurations containing multiple integrated computational elements include, for example, disposing the integrated computational elements along an extended optical train or housing the integrated computational elements on a movable assembly that allows different integrated computational elements to be exposed to electromagnetic radiation at various points in time (e.g., through lateral or rotational motion of the movable assembly). Either device configuration, however, can result in an operational profile that is too bulky to fit effectively within confined locales. In addition to the space occupied by a movable assembly itself, the operating mechanisms needed to produce lateral or rotational motion can sometimes exceed the available space in confined locales, such the space within or in proximity to a tubular string within a subterranean wellbore. Furthermore, extreme downhole operating conditions can also be taxing to such operating mechanisms and the necessity to supply power downhole thereto can be problematic in many aspects.